1. Field of the Invention
The present invention relates to compositions useful for coating various surfaces, including, metals, especially aluminum, steel and galvanized steel, and various metal alloys, such as brass, alkali metal silicate coatings, priming metals, painted finishes, marine finishes, and the like. More particularly, this invention relates to silane-based, coating compositions which are catalyzed with acid and/or base metallic and/or non-metallic compounds and which form strongly adherent, corrosion resistant coatings on a wide range of painted and non-painted surfaces, including metals, plastics, concrete and alkali metal silicates. Coating compositions of this invention provide hard, transparent, durable coatings which do not suffer noticeable degradation in gloss nor concurrent yellowing over long periods of time under exposure to corrosive, e.g., acidic or alkaline conditions.
2. Discussion of the Prior Art
It is well known to catalyze silanes with acids. However, acid catalyzed aqueous silane coating compositions are not considered useful for coating steel; the acid conditions, e.g., pH below 7, promote corrosion of the steel substrate.
U.S. Pat. Nos. 3,944,702, 3,976,497, 3,986,997 and 4,027,073 describe coating compositions, which are acid dispersions of colloidal silica and hydroxylated silsequioxane in an alcohol-water medium.
U.S. Pat. No. 4,113,665 discloses chemically resistant ambient curable coatings based on a binder of which the major portion is prepared by reacting, in an acidic solution, trialkoxysilanes (e.g., methyltriethoxysilane) with aliphatic polyols, silicones or both. Barium fillers, such as barium metaborate, may be added to provide resistance to sulfur dioxide. Zinc oxide or metallic zinc may be included for further corrosion resistance. The compositions may be applied to, e.g., steel petroleum tanks, by spraying, concrete, vitreous surfaces.
U.S. Pat. No. 4,413,086 describes water reducible coating compositions containing organosilanepolyol which is a reaction product between certain hydrophilic organic polycarbinols and organosilicon material, e.g., organosilane, curing agent (e.g., aminoplast resin), organic solvent (optional), essentially unreacted polyol (optional), essentially unreacted hydrolyzed and condensed organosilane (optional), water (optional) and pigment (optional).
U.S. Pat. No. 4,648,904 describes an aqueous emulsion of (a) hydrolyzable silane, inclusive of methyltrimethoxysilane, (b) surfactant (e.g., Table I, col. 4) and (c) water. The coatings may be used for rendering masonry water repellant.
U.S. Pat. No. 5,275,645 is purported to provide an improvement to the acid-catalyzed organosilane coating compositions of the above-mentioned U.S. Pat. No. 4,113,665. According to this patent a protective coating is obtained at ambient temperature from a coating composition containing organosilanes having an Sixe2x80x94O bond, using an amine catalyst and an organometallic catalyst.
U.S. Pat. No. 5,879,437 describes a coating composition containing a tetraalkyl silicate or monomeric or oligomeric hydrolysis product thereof, present in a proportion of 40-90% by weight based on the non-volatile content of the composition and a hydrous oxide sol (Type A or Type B), in an amount such that the oxide constitutes 10-60% by weight of the non-volatiles. According to the patentees, this coating composition is suitable for the pretreatment of solid surfaces such as metals generally, including steel, titanium, copper, zinc and, particularly aluminum, to improve adhesion properties of the pretreated surface to subsequently applied coatings, such as paint, varnish, lacquer; or of adhesive, either in the presence or absence of a lubricant.
U.S. Pat. No. 5,882,543 describes methods and compositions for dehydrating, passivating and coating HVAC and refrigeration systems. The compositions include an organometalloid and/or organometallic compound, which reacts with water in the system. The sealing function of these compositions is apparently obtained by introducing the composition to the fluid enclosure and upon exiting from an opening, the composition (i.e., organometallic) reacts with atmospheric moisture to seal the opening.
U.S. Pat. No. 5,939,197 describes sol-gel coated metals, especially titanium and aluminum alloys. The sol-gel coating provides an interface for improving adhesion, through a hybrid organometallic coupling agent at the metal surface, between the metal and an organic matrix resin or adhesive. The sol is preferably a dilute solution of a stabilized alkoxyzirconium organometallic salt, such as tetra-i-propoxy-zirconium, and an organosilane coupling agent, such as 3-glycidyloxypropyltrimethoxysilane, with an acetic acid catalyst.
U.S. Pat. No. 5,954,869 discloses an antimicrobial coating from water-stabilized organosilanes obtained by mixing an organosilane having one or more hydrolyzable groups, with a polyol containing at least two hydroxyl groups. This patent includes a broad disclosure of potential applications and end uses, e.g., column 4, lines 35-53; columns 23-25.
U.S. Pat. No. 5,959,014 relates to organosilane coatings purported to have extended shelf life. Organosilane of formula RnSiX4-n (n=0-3; R=non-hydrolyzable group; X=hydrolyzable group) is reacted with a polyol containing at least three hydroxyl groups, wherein at least any two of the at least three hydroxyl groups are separated by at least three intervening atoms.
U.S. Pat. No. 6,057,040 relates to novel bis-aminosilanes and coating compositions containing the bis-aminosilanes.
In my recently issued U.S. Pat. No. 5,929,129, there are described corrosion resistant coatings provided by aqueous-alcoholic dispersions of the partial condensate of monomethyl silanol (obtained by hydrolysis of monomethyl alkoxysilane) alone or in admixture with minor amounts of other silanol, e.g., gamma-glycidyloxy silanol, wherein the reaction is catalyzed by divalent metal ions, e.g., Ca+2, typically from alkaline earth metal oxides. When these coating are applied to, e.g., boat hulls, such as aluminum hulls, they are highly effective in preventing corrosion from salt water for extended periods.
The coating compositions of this earlier patent, have also been found to be very highly effective in providing strongly adherent, corrosion resistant coatings on a variety of other substrates and products, including, especially, air conditioning and other HVAC systems (see, e.g., Provisional Application 60/181061, filed Feb. 8, 2000, in the names of Anthony Gedeon, et al.).
In my Provisional Application, Ser. No. 60/185,354, filed Feb. 28, 2000, silane-based, aqueous coating compositions are described which are especially adapted for coating or overcoating refurbished painted finishes, especially as a gel-coat restorative for fiberglass-reinforced epoxy and polyester resins, particularly, for boat hulls and other marine finishes. According to this Provisional application, an acidic aqueous silane based coating composition is described which is obtained by admixing (A) at least one silane of the formula (1)
R1Si(OR2)3xe2x80x83xe2x80x83(1)
wherein
R1 is a lower alkyl group, a phenyl group or an
N-(2-aminoethyl)-3-aminopropyl group, and
R2 is a lower alkyl group;
(B) acid component selected from water-soluble organic acids, H3BO3 and H3PO3; and
(C) water.
Other ingredients which can be used in these compositions include silicates, mono-lower alkyl ethers of ethylene glycol, lower alkanol, ultraviolet light absorbers, colloidal aluminum hydroxides and metal alcoholates.
In my provisional application Ser. No. 60/185,367, filed Feb. 28, 2000, I described non-aqueous coating compositions containing, for example, (A) silanes represented by formula (1):
R1nSi(OR2)4-nxe2x80x83xe2x80x83(I)
where R1 is a lower alkyl group, phenyl group, 3,3,3-trifluoropropyl group, xcex3-glycidyloxypropyl, xcex3-methacryloxypropyl group, N-(2-aminoethyl)-3-aminopropyl group or aminopropyl group,
R2 is a lower alkyl group; and
n is a number of 1 or 2;
(B) vinyltriacetoxysilane and/or colloidal aluminum hydroxide and/or at least one metal alcoholate of formula (2):
M(OR3)mxe2x80x83xe2x80x83(2)
where M is a metal of valence m, R3 is a lower alkyl group; and n is a number of 2 to 4. In other embodiments, the compositions may further include one or more of (C) ethylortho-silicate, ethylpolysilicate or colloidal silica dispersed in lower alkanol; (D) boric acid, optionally dissolved in lower alkanol; (E) xcex3-glycidyloxypropyltrimethoxysilane; (F) finely divided solid lubricant.
In addition to the immediately above described compositions, which form part of the present invention, there is still a need to provide corrosion resistant coatings which do not require acidic pH""s to catalyze the polymerization of silanols to form polysiloxane coatings and which may be applied to steel or other acid degradable surfaces.
There is also a need to provide coating compositions with improved pot life, namely, slow polymerization rates.
There is also a need to provide silane based aqueous coating compositions which are effective to overcoat silicate coatings.
It would also be advantageous to provide silane based aqueous coating compositions which do not include or require surfactants or emulsifiers.
More generally, there is still a need in the coating art for coating compositions which are easy to apply to various metallic or non-metallic substrates and which provide improvements in durability, including adhesion to the substrate, corrosion resistance to acids, alkalis and solvents, and other improved properties, such as transparency, freedom from gellation, storage stability, and the like.
The foregoing and other objects of this invention are described in further detail below.
Accordingly, this invention provides compositions effective for coating a wide range of metallic and/or non-metallic surfaces, including steel, galvanized steel, brass, aluminum, alkali metal silicates, glass, fiberglass, painted surfaces and the like.
In accordance with one embodiment hereof, an aqueous coating composition is formed by admixing the following ingredients (A), one or both of (B) and/or (C), and (D):
(A) at least one silane of the formula (1)
R1Si(OR2)3xe2x80x83xe2x80x83(1)
xe2x80x83wherein
R2 is a lower alkyl group, a phenyl group or a functional group, including at least one of vinyl, acrylic, amino, mercapto, or vinyl chloride functional group; and
R2 is a lower alkyl group;
(B) base component;
(C) acid component selected from the group consisting of alkanoic acid having from about 1 to about 5 carbon atoms, H3BO3 and H3PO3; and
(D) water.
The composition may further comprise (E) epoxy silane. Especially when component (C) is present, the composition may also further comprise an hydroxide or carbonate of magnesium, calcium or zinc. When component (B) is present, the base component may be aminosilane, such as, for example, 3-(2-aminoethylamino)propyltrimethoxysilane or 3-aminopropyltrimethoxysilane. The composition with components (B) and/or (C) may further comprise one or more of, for example, (E) epoxysilane; (F) alkali metal silicate component, which may be hydrolyzed; (G) mono-lower alkyl ether of ethylene glycol; (H) lower alkanol; (I) ultra-violet light absorber; (J) (i) colloidal aluminum hydroxide or (J)(ii) metal alcoholate of formula (2)
M(OR3)mxe2x80x83xe2x80x83(2)
where M represents a metal of valence m, each R3 independently represents lower alkyl; and m is an integer of 3 or 4 or both (J)(i) and (J)(ii); (K) a color forming silane hydrolysis catalyst, such as, for example, chromium acetate hydroxide.
In accordance with another embodiment of the invention, there is provided an aqueous coating composition formed by admixing (A) at least one silane of formula (1) given above; (D) water; (J) (i) colloidal aluminum hydroxide or (ii) metal alcoholate of formula (2) M(OR3)m wherein M is a metal of valence m, R3 is a lower alkyl group, and m is 3 or 4, or (iii) a mixture of (i) and (ii); and, optionally, a silane hydrolyzing catalyst, effective to inhibit gellation and extend storage life and pot life, such as epoxide silane.
In accordance with still yet another embodiment of the invention, there is provided an aqueous coating composition formed by admixing (A) at least one silane of formula (1) given above; (H) lower alkanol solvent; (D) water; (K) chromium acetate hydroxide or other silane polymerization catalyst which provides coloration to the resulting coating.
Another embodiment provided by the present invention is an aqueous coating composition formed by admixing (A) at least one silane of formula (1) given above; (D) water; (F) alkali metal silicate, optionally pre-hydrolyzed; (H) lower alkanol as solvent; and (J) (i) colloidal aluminum hydroxide or (ii) metal alcoholate of formula (2) given above or (iii) a mixture of (i) and (ii).
In another embodiment of the invention there is provided a non-metallic aqueous coating composition formed by admixing (A) at least one silane of formula (1) given above; (B) a basic amine silane catalyst, such as 3-(2-aminoethylamino)propyltrimethoxy silane or 3-aminopropyltrimethoxy silane; (D) water; (E) epoxide silane; (H) lower alkanol solvent.
The present invention further provides an aqueous coating composition containing mixed valence silane catalysts. According to this embodiment of the invention, an aqueous coating composition is formed by admixing (A) at least one silane of formula (1) given above; (B) at least one compound comprising an hydroxide or carbonate of a divalent metal, such as calcium or magnesium; (C) boric acid or phosphorous acid; (D) water; (E) ethyl polysiloxane; (H) lower alkanol solvent, and (J) a metal alcoholate of formula (2) above, wherein M represents a tetravalent metal, i.e., m=4, such as, for example, tetrabutoxytitanate.
In still yet another aspect of the invention there is provide an aqueous alcoholic coating composition effective for providing clear, hard and strongly adherent corrosion resistant coatings for glass substrates and for providing clear, hard, glossy and slick (slippery or wax-like) adherent corrosion resistant coatings for metal substrates, such as automobiles and other vehicles. According to this aspect of the invention, there is provided a coating composition which is an alcoholic solution containing as the essential and major film-forming components a mixture of silane compounds of the above formula (1) wherein the R1 group in one silane compound is the lower alkyl group and in another silane compound the R1 group is an aryl group, especially, a phenyl group. The composition also includes small amounts of an alcohol soluble activator, such as, tetramethylammonium hydroxide or calcium hydroxide, which functions, on glass, as an abrasive agent and etchant, and a silicate, preferably, partially hydrolyzed silicate, especially a hydrolysis product of tetraethylsilicate. The non-aqueous compositions may additionally include as an optional but preferred ingredient, xcex3-glycidyloxypropyltrimethoxysilane or other epoxysilane compound.
According to the present invention, the non-aqueous composition as described in the previous paragraph may be applied to a substrate, such as glass window (particularly, the outside surface of the glass window), or to the painted finish of an automobile, by wiping with a brush, sponge, or soft cloth. After allowing the alcohol to evaporate, leaving a whitish or chalky finish, due to the Ca(OH)2 particles deposited on the surface, the coating is polished to provide a highly transparent hard adherent finish. When applied to a painted metal surface, such as an automobile, the coating becomes slick and glossy, providing a highly durable finish, much superior to known wax finishes. For optimum results, it may be and generally is necessary to thoroughly pre-clean the surface to be coated.
The invention also provides the novel coatings obtained from any of the above aqueous coating compositions and the coated articles obtained there from.
In still another aspect of the invention, there is provided a coating composition which is highly effective as a primer for steel, galvanized steel, aluminum and other metal surfaces. According to this aspect of the invention the primer coating composition contains as the essential ingredients at least two polyfunctional organosilane compounds, such as, an aminoalkylaminoalkyltrialkoxysilane and an epoxy silane in a volatile organic solvent, especially lower alkanol solvent. The alcohol or other organic solvent mixture of the polyfunctional silane compounds is combined with a small quantity of water, as silane hydrolyzing catalyst. These primer coating compositions are free from silica and are also free from monofunctional silanes.
The present invention, including specific applications thereof, will now be described in further detail by way of specific embodiments and examples, although the invention is not limited to these specific embodiments.
According to one embodiment of this invention, a coating composition is formed by admixing
(A) at least one silane of the formula (1)
R1Si(OR2)3xe2x80x83xe2x80x83(1)
xe2x80x83wherein
R1 is alkyl, preferably, a C1-C6 alkyl group (the group may be a straight, cyclic, or branched-chain alkyl), such as methyl, ethyl, n- or iso-propyl, n- or iso-butyl, n-pentyl, cyclohexyl, and the like, preferably a C1-C4 alkyl group, most preferably a methyl, ethyl, propyl or butyl group), aryl, such as a phenyl, or a functional group or groups, such as vinyl, acrylic, methacrylic, amino, mercapto, or vinyl chloride functional group, and each R2 is, independently, an alkyl group (i.e. a C1-C6 straight or branched chain alkyl group, preferably a C1-C4 alkyl group, such as a methyl group);
(B) base component selected from calcium, zinc and aluminum hydroxides;
(C) acid component selected from the group consisting of water-soluble organic acids (preferably alkanoic acid such as formic acid, acetic acid, propanoic acid or butyric acid, most preferably acetic acid), H3BO3 (boric acid) and H3PO3 (phosphorous acid); and
(D) water.
As examples of silanes of formula (1), wherein R1 is an alkyl group or aryl group, mention may be made of, for example, methyltrimethoxysilane, ethyltrimethoxysilane, ethyltriethoxysilane, n-propyltrimethoxysilane, n-propyltriethoxysilane, isopropyltrimethoxy silane, n-butyltrimethoxy silane, isobutyltrimethoxy silane, phenyltrimethoxy silane, preferably methyltrimethoxy silane. In the case where R1 is a functional group, mention may be made, for example, of N-(2-aminoethyl)-3-aminopropyltrimethoxy silane, 3-mercaptopropyltrimethoxy silane, 3-mercaptopropyltriethoxy silane, 3-aminopropyltriethoxy silane, 3-(meth)acryloxypropyl trimethoxy silane, 3-(meth)acryloxypropyltriethoxy silane, n-phenylaminopropyltrimethoxy silane, vinyltriethyoxy silane, vinyltrimethoxy silane, allyltrimethoxy silane, and any of the aminosilane catalysts, described herein below as component (B1).
As used herein, the expression xe2x80x9cfunctional groupxe2x80x9d is intended to include any group, other than hydroxyl, (including alkoxy, aryloxy, etc.), which is hydrolyzable to provide, in situ, a reactive group (e.g., reactive hydrogen) which will react, in other than a condensation reaction, with the substrate (e.g., metal), itself, or other reactive components in or from the coating composition.
The functional groups, in addition to the hydroxyl group (by hydrolysis of the (OR2) groups), tend to form three-dimensional or cross-linked structure, as well known in the art.
Moreover, in the various embodiments of the invention, it is often preferred to use mixtures of two or more silane compounds of formula (1). Mixtures of at least phenyltrimethoxysilane and methyltrimethoxysilane are often especially preferred.
Generally, total amounts of silane compounds of formula (1) will fall within the range of from about 40 to about 90 percent by weight, preferably from about 50 to about 85 percent by weight, based on the total weight of silanes, acid component and water.
In addition to silane compound(s) of formula (1), the composition may additionally include a bistrifunctional aminosilane, such as represented by the following formula (4):
X[R1Si(OR2)3]2xe2x80x83xe2x80x83(4)
where R1 and R2 are as defined above, and X represents an amino group (xe2x80x94NH) or keto group 
as a basic catalyst, not requiring acid stabilization. As a representative example of aminosilane or ketosilane catalyst according to formula (4), mention may be made of, for example, bis(trimethoxypropylsilane) amine, bis(trimethoxyethylsilane) amine, di(trimethoxybutylsilane) ketone, di(trimethoxypropylsilane) ketone, and the like. The silane compounds of formula (4) function as a less active basic catalyst, not requiring acidic passivation. Minor amounts, usually from about 1 to about 10 parts, preferably, from about 2 to about 8 parts, of compound of formula (4) per 100 parts of silane compound(s) of formula (1) provide satisfactory results.
The base component (B) may be, for example, an inorganic base, such as, for example, calcium hydroxide, aluminum hydroxide or zinc hydroxide, or mixture thereof; or an organic base component, such as, for example, aminosilane.
The amount of the base component is generally, up to about 2%, such as, for example, from about 0.1 to 2.0%, by weight of the composition, especially, from about 0.2 to 1.6%.
As examples of the acid component (C), mention may be made of lower alkanoic acids, such as, for example, formic acid, acetic acid, propanoic acid, butyric acid, and inorganic acids, such as, for example, boric acid (H3BO3) or ortho-phosphorous acid (H3PO3), preferably acetic acid, boric acid or ortho-phosphorous acid, most preferably, for reasons of economy and safety, acetic acid. The acid may be added as free acid or as inorganic salt thereof, such as alkali metal (e.g., sodium), alkaline earth metal (e.g., calcium), or ammonium salt.
Generally, total amounts of the inorganic acid component will fall within the range of from about 0.3 to about 4 percent by weight, preferably from about 0.5 to about 3%, preferably, from about 0.5 to about 2.5 percent by weight, based on the total weight of silanes, acid component and water. For acetic acid, the preferred range is from about 0.1 to about 1.0 percent, preferably, from about 0.2 to about 0.7 percent, by weight, based on the total weight of the composition.
Generally, the total amount of water will fall within the range of from about 10 to about 60 percent by weight, preferably from about 10 to about 45 percent by weight, based on the total weight of silanes, acid component and water.
Some or all of the water may be provided by the acid component, when the base or acid component is supplied as an aqueous solution, e.g., 5% aqueous solution of ortho-phosphorous acid or saturated aqueous solution of boric acid (about 6% by weight of H3BO3).
Since the presence of metallic and other impurities may have an adverse effect on the properties of the resulting coatings, preferably, the water is distilled or de-ionized water.
While general and preferred ranges of amount for the film-forming and catalytic components have been described above, it will be recognized by those skilled in the art, that these amounts may be increased or decreased as necessity demands and that the optimum amounts for any particular end use application may be determined by the desired performance. In this regard, for example, when the amount of catalyst is reduced, the time to achieve freedom from tack will increase. Similarly, when the amount of the catalyst(s) is (are) increased, this may lead to increased rates of cracking, loss of adhesion and performance loss of the resulting coating.
The compositions of this embodiment may further include one or more additional additives for functional and/or esthetics effects, such as, for example, silicates, organic solvents and co-solvents, UV absorbers, metal catalysts and the like.
The above-noted optional ingredients may be used singly or in any combination in the coating composition of this invention.
As examples of silicate component, mention may be made of ethyl or methyl orthosilicate or ethyl polysilicate. These silicates may be hydrolyzed, for example, from about 28% to about 52% silica. Especially preferred in this regard is tetraethylsilicate (TEOS) which has been subjected to controlled hydrolysis, providing a mixture of TEOS and, from about 20% to about 60% polydiethoxysilane oligomers. For example, a 50% hydrolysis product may be referred to herein as xe2x80x9cpolydiethoxysilane (50%).xe2x80x9d
Generally, total amounts of silicate component, when used, will fall within the range of from 0 to about 45 percent by weight, preferably from 0 to about 25 percent by weight, based on the total weight of silanes, acid component and water.
As examples of mono-lower alkyl ether of alkylene (e.g., ethylene) glycol, mention may be made of mono-C1-C6-alkyl ethers of ethylene glycol, such as, for example, monomethyl ether, monoethyl ether, monopropyl ether, monobutylether, monopentylether or monohexylether, preferably monoethyl ether of ethylene glycol.
Generally, total amounts of the mono-lower alkyl ether of ethylene glycol, when used, will fall within the range of from 0 to about 15 percent by weight, preferably from 0 to about 6 percent by weight, based on the total weight of silanes, acid component and water.
As an example of ultra-violet light absorber, mention may be made of titanium dioxide in finely powdered form, e.g., having an average particle diameter of about 20 nm. Other inorganic or organic ultra-violet light absorbers may be utilized in so far as they do not interfere with the objects of this invention.
Generally, total amounts of the ultra-violet light absorber, when used, will fall within the range of from 0 to about 10 percent by weight, preferably from 0 to about 5 percent by weight, based on the total weight of silanes, acid component and water.
As examples of organic solvents, mention may be made of lower alkanol, e.g., C2-C4 alkanols, preferably isopropanol. Other organic solvents, such as, for example, acetone, methyl ethyl ketone, ethyl acetate, and the like may also be used. Generally, total amounts of organic solvent, such as, lower alkanol, will fall within a range of from 0 to about 50 percent by weight, preferably from 0 to about 30 percent by weight, based on the total weight of silane(s), acid component and/or base component and water. In some cases, however, substantially higher amounts may be convenient, especially where, for example, the coating compositions are applied by spraying as an aerosol or mist.
As examples of the metal catalysts, mention may be made of (i) colloidal aluminum hydroxide, (ii) metal alcoholates, such as those represented by the following formula (2):
M(OR3)mxe2x80x83xe2x80x83(2)
where M is a metal of valence m (namely, from Groups IIIA, IVA, IIB or IVB of the periodic table of the elements), e.g., boron, titanium, aluminum, indium, yttrium, cerium, lanthanum, silicon, tin, hafnium, etc; boron, aluminum and titanium are especially preferred because the alkoxides of these metals are more readily commercially available, and tend to be non-toxic);
R3 is a lower alkyl group, e.g., C1-C6 straight or branched chain alkyl group, preferably C2-C4 alkyl group, most preferably, isopropyl, isobutyl or n-butyl; and
m is an integer of 3 or 4.
As specific examples of the metal alcoholates of formula (2), mention may be made of titanium alcoholates of C2-C4 alkanols, e.g., titanium tetraisopropoxide and titanium tetrabutoxide.
In addition, double metal alcoholates of, for example, AlTi, AlZr, AlY, MgAl, MgTi, MgZr, etc., may also be used.
The presence of the trivalent and tetravalent metal ions are especially useful for coating compositions applied to steel since they tend to form insoluble (water and alkali) iron silicates, whereas the products of divalent metals, tend to be soluble.
Generally, total amounts of the colloidal aluminum hydroxide and/or metal alcoholate, when used, will fall within the range of from 0 to about 2.5 percent by weight, preferably from 0 to about 1 percent by weight, based on the total weight of silanes, acid component and water.
Within the above general proportions, the silane component (A) may be used in an amount of from about 15 to about 25 parts by weight, preferably as a mixture of from about 15 to about 20 parts by weight of methyltrimethoxysilane and from about 1 to about 5 parts by weight of phenyltrimethoxysilane; the base component (B), when present, is used in an amount of from about 0.1 to 3 weight percent, preferably from about 0.2 to 2.5 weight percent; the acid component (C), when present, is used in an amount of from about 0.2 to about 0.8 part by weight; the water (D) is used in an amount of from about 2.5 parts by weight to about 22 parts by weight; the silicate component is used in an amount of from 0 to about 15 parts by weight; the mono-lower alkyl ether of ethylene glycol is used in an amount of from 0 to about 3 parts by weight; the ultra-violet light absorber is used in an amount of from 0 to about 2 parts by weight; and lower alkanol is used in an amount of from 0 to about 20 parts by weight; and the colloidal aluminum hydroxide and/or the metal alcoholate is used in an amount of from 0 to about 0.5 part by weight.
According to a particularly preferred embodiment of the present invention, the coating compositions may include metal catalysts which additionally provide a tint or coloration to the resulting coating. Chromium acetate hydroxide is especially useful in this regard, serving as a basic catalyst which provides a bluish tint to the resulting coating. This feature may be especially useful, for example, in connection with providing corrosion resistant coatings to articles having large surface areas and/or difficultly accessible regions, where visibility of the applied coating can assure total coverage of the areas to be coated while avoiding wasting coating by excessive applications over already coated surfaces. For instance, addition of the chromium acetate hydroxide catalyst has been successfully applied to coatings for air conditioning units and other HVAC and heat transfer coils and products, as described in Provisional Application No. 60/236,158, filed Feb. 8, 2000, and its corresponding non-Provisional Application, filed on even date herewith, titled xe2x80x9cMETHOD FOR IMPROVING HEAT EFFICIENCY USING SILANE COATINGS AND COATED ARTICLES PRODUCED THEREBYxe2x80x9d, under attorney docket number GED-6.
Other basic metal catalysts providing a colorant function include, for example, iron acetate, iron acetate hydroxide, chromium acetate, and the like. Other metal compounds such as compounds of antimony, lead, barium, etc., also form colored products, but tend to be more toxic and, therefore, less useful for general purposes.
The present coating composition may be formed by mixing the above-noted components and allowing them to react. A suitable reaction time is typically 4 to 12 hours, if no colloidal aluminum hydroxide and/or metal alcoholate is present. Shorter reaction times may be obtained in the presence of colloidal aluminum hydroxide and/or metal alcoholate.
If no lower alkanol is present, frequent shaking may be necessary to achieve a shorter reaction time.
For ease of handling, the coating composition may be provided as a two or three container system, e.g., the silane component and any silicate component, if present, being provided in a first container and all other components being provided in a second or second and third container. The water may be provided separately from the other components. The contents of the two or three containers may be mixed shortly prior to use and allowed to react for an appropriate reaction time, as noted above.
In accordance with another embodiment of the invention, especially suitable for use in coating steel based substrates, because no acid component is used, a coating composition is prepared by admixing
(A) at least one silane of the formula (1)
R1Si(OR2)3xe2x80x83xe2x80x83(1)
xe2x80x83wherein R1 and R2 are as defined above,
(B) base component, especially hydroxides of calcium, zinc, and aluminum;
(E) epoxysilane; and
(D) water.
In this embodiment, the components (A), (B) and (E) may be any of those described above in connection with the first embodiment. Similarly, one or more of the other optional ingredients, including, for example, the amino or keto silane compounds of formula (4), silicate component (F), metal alcoholate catalyst of formula (2), monoloweralkyl ether of alkylene glycol, UV absorbers, solvents and co-solvents, etc., which may be included in the coating compositions of the first embodiment may similarly be used in the coating compositions of the second embodiment.
As the epoxy silane, component (E), mention may be made of, for example, glycidoxy(C1-C6-alkyl)(tri-C1-C3alkoxy)silane, such as, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropyldiisopropylethoxysilane, (3-glycidoxypropyl)methyldiethoxysilane, 3-glycidoxypropyltriethoxysilane, and epoxy-functional silane compounds represented by the formula (3) 
wherein R10, R20 and R30, independently, represent aliphatic or aromatic groups, especially, lower alkyl of from 1 to 6 carbon atoms, preferably C1-C3 alkyl;
EP represents glycidyl (e.g., glycidyloxy), cyclohexane oxide (epoxycyclohexyl) or cyclopentane-oxide (epoxycyclopentyl); and
n is a number of from I to 4, preferably 1, 2 or 3.
As examples of the epoxy functional compounds represented by formula (3), mention may be made of, for example, gamma-glycidyloxymethyltrimethoxysilane, gamma-glycidyloxymethyltriethoxysilane, gamma-glycidoxymethyl-tripropoxysilane, gamma-glycidoxymethyl-tributoxysilane, beta-glycidoxyethyltrimethoxysilane, beta-glycidoxyethyltriethoxysilane, beta-glycidoxyethyl-tripropoxysilane, beta-glycidoxyethyl-tributoxysilane, beta-glycidoxyethyltrimethoxysilane, alpha-glycidoxyethyl-triethoxysilane, alpha-glycidoxyethyl-tripropoxysilane, alpha-glycidoxyethyltributoxysilane, gamma-glycidoxypropyl-trimethoxysilane, gamma-glycidoxypropyl-triethoxysilane, gamma-glycidoxypropyl-tripropoxysilane, gamma-glycidoxypropyltributoxysilane, beta-glycidoxypropyl-trimethoxysilane, beta-glycidoxypropyl-triethoxysilane, beta-glycidoxypropyl-tripropoxysilane, beta-glycidoxypropyl-tributoxysilane, alpha-glycidoxypropyl-trimethoxysilane, alpha-glycidoxypropyl-triethoxysilane, alpha-glycidoxypropyl-tripropoxysilane, alpha-glycidoxypropyl-tributoxysilane, gamma-glycidoxybutyl-trimethoxysilane, delta-glycidoxybutyl-triethoxysilane, delta-glycidoxybutyl-tripropoxysilane, delta-glycidoxybutyl-tributoxysilane, delta-glycidoxybutyl-trimethoxysilane, gamma-glycidoxybutyl-triethoxysilane, gamma-glycidoxybutyl-tripropoxysilane, gamma-alpropoxybutyl-tributoxysilane, delta-glycidoxybutyl-trimethoxysilane, delta-glycidoxybutyl-triethoxysilane, delta-glycidoxybutyl-tripropoxysilane, alpha-glycidoxybutyl-trimethoxysilane, alpha-glycidoxybutyl-triethoxysilane, alpha-glycidoxybutyl-tripropoxysilane, alpha-glycidoxybutyl-tributoxysilane, (3,4-epoxycyclohexyl)-methyl-trimethoxysilane, (3,4-epoxycyclohexyl)methyl-triethoxysilane, (3,4-epoxycyclohexyl)methyl-tripropoxysilane, (3,4-epoxycyclohexyl)-methyl-tributoxysilane, (3,4-epoxycyclohexyl)ethyl-trimethoxysilane, (3,4-epoxycyclohexyl)ethyl-triethoxysilane, (3,4-epoxycyclohexyl)ethyl-tripropoxysilane, (3,4-epoxycyclohexyl)-ethyl-tributoxysilane, (3,4-epoxycyclohexyl)propyl-trimethoxysilane, (3,4-epoxycyclohexyl)propyl-triethoxysilane, (3,4-epoxycyclohexyl)propyl-tripropoxysilane, (3,4-epoxycyclohexyl)propyl-tributoxysilane, (3,4-epoxycyclohexyl)butyl-trimethoxysilane, (3,4-epoxycyclohexyl)butyl-triethoxysilane, (3,4-epoxycyclohexyl)butyl-tripropoxysilane, (3,4-epoxycyclohexyl)butyl-tributoxysilane.
The amount of the components (A), (B) and (D) may generally be the same amounts as previously disclosed for the first embodiment.
The amount of component (E) epoxysilane will generally be within the range of from about 1 to about 22 percent by weight, preferably, from about 2 to 16% by weight, based on the total weight of the composition.
According to still another embodiment of the invention, an aqueous silane-based coating composition is formed by admixing as component (A) at least one organosilane of formula (1), as given above; (D) water; (J) (i) colloidal aluminum hydroxide or (ii) metal alcoholate of the previously given formula (2) or a mixture of (i) and (ii). Additional silane hydrolyzing catalyst, including, for example, the compound of formula (4), or any of the other disclosed aminosilane catalysts, effective to inhibit gellation, may also be added in order to inhibit gellation and, thereby extend storage life and pot life.
As examples of the organosilanes of formula (1) and metal alcoholate of formula (2) the same compounds as mentioned above may be used. Generally, the amount of organosilane(s) of formula (1) will be from about 10 to 50%, preferably, 12 to 35%, and the amount of the component (J) will be from about 0.05 to about 1.0 percent, preferably, from about 0.1 to about 0.8%, each based on the total weight of the composition.
Representative of the additional silane hydrolyzing agent and gellation inhibitor, the aforementioned epoxide silanes (E) are especially preferred.
In another embodiment, an aqueous organosilane coating composition is formed by admixing (A) at least one organosilane of formula (1); (H) lower alkanol solvent; (D) water; and (K) chromium acetate hydroxide or other silane polymerization catalyst which will provide coloration to the resulting coating.
The amount of the component (K) is, usually, up to about 2 percent by weight of the coating composition, preferably from about 0.1 to about 1.8%, especially, from about 0.4 to about 1.3% by weight, based on the total weight of the coating composition.
Here again, one or more optional ingredients, such as those discussed in connection with other embodiments, may also be included in the compositions of this embodiment.
According to another embodiment of the invention, an aqueous based organosilane coating composition is formed by admixing (A) at least one organosilane of formula (1); (D) water; (F) alkali metal silicate, preferably pre-hydrolyzed; (H) lower alkanol solvent; (J) (i) the aforementioned metal catalyst (i) colloidal aluminum hydroxide; (ii) metal alcoholate of formula (2) as given above, or (iii) mixture of (i) and (ii).
The components of the compositions of this embodiment, like those of the previous alternatives, may be selected from the same components and in the same amounts as previously described.
In accordance with still another embodiment of the invention, an aqueous organosilane coating composition is formed by admixing (A) at least one organosilane of formula (1); (Bxe2x80x2) at least one basic amine silane catalyst, (D) water, (E) epoxide silane: and (H) lower alkanol solvent.
As examples of the basic amine silane catalyst, (Bxe2x80x2), mention may be made of, for example, aminoethyl-triethoxysilane, beta-amino-ethyltrimethoxysilane, beta-aminoethyl-triethoxysilane, beta-amino-ethyl-tributoxysilane, beta-aminoethyltripropoxysilane, alpha-aminoethyl-trimethoxysilane, alpha-aminoethyl-triethoxysilane, gamma-aminopropyltrimethoxysilane, gamma-aminopropyl-triethoxysilane, gamma-aminopropyl-tributoxysilane, gamma-amino-propyltripropoxysilane, beta-aminopropyl-trimethoxysilane, beta-aminopropyl-triethoxysilane, beta-amino-propyltripropoxysilane, beta-aminopropyl-tributoxysilane, alpha-aminopropyl-trimethoxysilane, alpha-aminopropyltriethoxysilane, alpha-aminopropyl-tributoxysilane, alpha-aminopropyl-tripropoxysilane, N-aminomethylaminoethyl-trimethoxysilane, N-aminomethylaminomethyl-tripropoxysilane, N-aminomethyl-beta-aminoethyl-trimethoxysilane, N-aminomethyl-beta-aminoethyl-triethoxysilane, N-aminomethyl-beta-aminoethyl-tripropoxysilane, N-aminomethyl-gamma-aminopropyl-trimethoxysilane, N-aminomethyl-gamma-aminopropyl-triethoxysilane, N-aminomethyl-gamma-aminopropyl-tripropoxysilane, N-aminomethyl-beta-aminopropyl-trimethoxysilane, N-aminomethyl-beta-aminopropyl-triethoxysilane, N-aminomethyl-beta-aminopropyl-tripropoxysilane, N-aminopropyltripropoxysilane, N-aminopropyl-trimethoxysilane, N-(beta-aminoethyl)-beta-aminoethyl-trimethoxysilane, N-(beta-aminoethyl)-beta-aminoethyl-triethoxysilane, N-(beta-aminoethyl)-beta-aminoethyl-tripropoxysilane, N-(beta-aminoethyl)-beta-aminoethyl-trimethoxysilane, N-(beta-aminoethyl)-alpha-aminoethyl-triethoxysilane, N-(beta-aminoethyl)-alpha-aminoethyl-tripropoxysilane, N-(beta-aminoethyl)-beta-aminopropyl-trimethoxysilane, N-(beta-aminoethyl)-gamma-aminopropyl-triethoxysilane, N-(beta-aminoethyl)-gamma-aminopropyl-tripropoxysilane, N-(beta-aminoethyl)-gamma-aminopropyl-trimethoxysilane, N-(beta-aminoethyl)-beta-aminopropyl-triethoxysilane, N-(beta-aminoethyl)-beta-aminopropyl-tripropoxysilane, N-(gamma-aminopropyl)-beta-aminoethyl-trimethoxysilane, N-(gamma-aminopropyl)-beta-aminoethyl-triethoxysilane, N-(gamma-aminopropyl)-beta-aminoethyl-tripropoxysilane, N-methyl aminopropyl trimethoxysilane, beta-aminopropyl methyl diethoxysilane, gamma-diethylene triaminepropyltriethoxysilane, and the like.
Of these, 3-(2-aminoethylamino)propyltrimethoxy silane [also known as N-(2-aminoethyl)-3-aminopropyltrimethoxysilane], and 3-aminopropyltrimethoxy silane, are especially preferred.
Aminosilanes of formula (4), above, may also be used.
For the components (A), (D), (E) and (H), the representative examples and amounts given above apply equally to this embodiment.
In accordance with still another embodiment of the invention, a multivalent catalyst system may be used to polymerize the organosilane of formula (1). For example, the mixed multivalent catalyst may include a divalent metal compound, such as hydroxide or carbonate of calcium, magnesium or other alkaline earth metal; a trivalent metal compound, such as, for example, boric acid or other compound of boron or aluminum; and a tetravalent metal compound, such as a compound of formula (2-a):
M1xe2x80x94(OR3)4xe2x80x83xe2x80x83(2-a)
where M1 represent a tetravalent metal, such as titanium, or zirconium, and R3 is as previously defined.
According to this embodiment, the proportions of the respective catalysts may be selected based on the desired properties but generally in terms of metal ions, weight ratios of M+2:M+3:M+4 of from about 0.1-1:0.05-1:0.1-2, preferably from about 0.4-1:0.2-1:0.5-1, provide good results.
The multivalent catalyst system may be used with any of the coating compositions described herein.
In one particular embodiment of the invention the subject formulations are aqueous alcoholic formulations effective for providing clear, hard and strongly adherent corrosion resistant coatings for glass substrates, e.g., windows, mirrors, counter-tops, table-tops, and the like, and also for providing clear, hard, glossy and slick (slippery or wax-like) adherent corrosion resistant coatings for metal surfaces, e.g., automobiles, trucks, buses, trains, and other vehicles, metal signs, and the like. According to this aspect of the invention, the coating composition contains as the essential and major film-forming components, a mixture of silane compounds of above formula (1), wherein R1 in a first silane compound is a lower alkyl group, such as methyl or ethyl while in a second silane compound, R1 is an aryl group, especially, phenyl. The ratio of the first silane compound to second silane compound is not particularly critical and may, generally, fall within a range of from about 3:1 to about 1:3, preferably, from about 1.5:1 to about 1:1.5, such as about 1:1, on a weight basis.
This composition will also include a small amount of moderately alcohol soluble to alcohol soluble basic activator for the silanes (either in the container, or in situ), especially, calcium hydroxide or tetramethylammonium hydroxide. Generally, an amount of calcium hydroxide, in the range of from about 0.4 to about 4, preferably, from about 1.2 to about 2.8 parts of basic activator, per 100 parts, in total, of silane compounds of formula (1), will provide satisfactory results. Since tetramethylammonium hydroxide tends to be more active and more soluble in alcohol than calcium hydroxide, smaller amounts of this basic activator, should be useful, for example, from about 0.01 to about 2, preferably, from about 0.02 to about 1 part of tetramethylammonium hydroxide, per about 100 parts of silane compounds of formula (1), should provide satisfactory results.
For this particular embodiment, it is expected that monovalent alkalis, such as, for example, sodium hydroxide, potassium hydroxide, and the like would be too active for easy application of the composition, while many other less active alkalies, could require addition of acid catalyst to promote the reaction, and therefore, would also not be preferred for the intended applications to glass or painted metal substrates.
These formulations also include a silicate, preferably, partially hydrolyzed silicate, such as, for example, hydrolysis product of tetraethylsilicate, e.g., polydiethoxysiloxane (about 50% solids). Amounts of the silicate, on a solids basis, per 100 parts of silane compounds of formula (1), will usually fall within the range of from about 1 to 16 parts, preferably, from about 2 to about 10 parts, more preferably, from about 4 to about 8 parts.
The film-forming and catalyst ingredients are added to lower alcohol solvent, preferably, isopropyl alcohol. Relatively dilute solutions facilitate application by wiping (e.g., using a soft cloth, sponge, etc.) or spraying. Generally, from about 600 up to about 1500 parts of alcohol per 100 parts of silane compounds of formula (1) provide satisfactory results.
An optional ingredient for this formulation is xcex3-glycidyloxypropyltrimethoxysilane, or other epoxy silane compound, such as mentioned above.
As described above, the coating compositions of this invention may be applied to a wide range of painted and non-painted metallic, non-metallic, e.g., siliceous, ceramic, vitreous substrates, including, for example, and not by way of limitation, iron, steel, aluminum, copper, brass, bronze, other alloys, plastics, e.g., polyolefins, polyesters, polyamides, polyimides, polycarbonates, polyetherimides, polysulfones, and the like, concrete, glass, alkali metal silicates, and the like. It is particularly advantageous that the compositions of this invention can be applied to even rusted metal substrates, e.g., rusted iron or steel, and still provide strongly adherent and durable, corrosion resistant coatings, especially if the substrate is prewashed, such as, for example, with a composition comprising water, isopropyl alcohol and acetic acid (e.g., from about 80 to about 95 parts, preferably about 85 to about 92 parts, e.g., 89 parts, water; from about 4.9 to about 19 parts, preferably about 8 to about 14 parts, e.g., 10 parts, isopropyl alcohol; and from about 0.1 to about 6, preferably about 0.5 to about 3, such as 1 part, acetic acid). The coating compositions of this invention when applied to a substrate, such as those mentioned herein, will readily penetrate even narrow and microscopic crevices or pores of the substrate, to form strong adherent bonds with the substrate. Although not wishing to be bound by any particular theory of operation, it is believed that the penetration and adherent bond formation is achieved, in part, because of the absence of large organic molecules from the invention coating systems.
The coating compositions contemplated herein may be formulated as solventless, aqueous or non-aqueous systems (although, in most cases, at least a catalytic amount of water is eventually added, directly or taken from the atmosphere). For example, the solventless systems may contain a mixture of methyltrimethoxysilane and phenyltrimethoxysilane and, catalyst, e.g., metal alcoholate, such as, for instance, tetrabutoxytitanate. The solventless systems have been applied to brass and bronze substrates to provide extremely durable and corrosion resistant coatings (i.e., withstanding exposure to over 4000 hours of salt water spray with no visible change). Suitable non-aqueous systems (e.g., by addition of small amounts of diluent, especially, lower alcohol, such as, isopropanol), may also be used, and such non-aqueous systems are described in the Applicant""s aforementioned commonly assigned co-pending Provisional application Ser. No. 60/185,367, filed Feb. 28, 2000, the disclosure of which is incorporated herein in its entirety, by reference thereto.
The coating composition may be applied in any conventional manner, preferably by dipping, wiping, brushing or spraying. Preferably, the spraying is carried out under an inert atmosphere, especially using dry N2 propellant, as a result of which extra gloss and hardness is imparted to the resulting coating. Although the reason for this has not been ascertained, it is presumed that nitrogen impacting the substrate surface removes at least some of the adsorbed oxygen and water, while at the same time, its positive Joule-Thomson coefficient retards solvent evaporation and promotes film generation. Therefore, since any such adsorbed oxygen and/or water would be expected to impair the qualities of the resultant coating, the removal thereof by the N2 gas stream, would tend to improve the qualities of the coating, including gloss and hardness.
The present invention also provides corrosion resistant primer coating compositions which are not only strongly adherent to a broad range of metal substrates, including, for example, aluminum, steel and galvanized steel, but also to a broad range of pigmented and unpigmented topcoat materials, including, for example, polyurethane resins, epoxy resins, acrylic resins, polyester resins, alkyd resins, polyetherpolyester resins, polycarbonate resins, and the like. Accordingly, the primer compositions of this invention can be used without any other tie-coat material.
According to this aspect of the invention, the primer composition is prepared by admixing two or more polyfunctional organosilanes as previously described. Monofunctional (e.g., organosilanes of formula (1) where R1 is alkyl or aryl) are not included in the primer composition. Silica and silicate or precursors thereof are also not included in the primer compositions.
At least one of the polyfunctional organosilanes will preferably include polyamino group as R1 in formula (1), namely, aminosilanes of the following formula (1-A)
H2Nxe2x80x94Raxe2x80x94NHxe2x80x94Rbxe2x80x94Si(OR2)3xe2x80x83xe2x80x83(1-A)
where Ra and Rb are each, independently, alkyl of from 1 to 6 carbon atoms, preferably 1 to 4 carbon atoms, especially 2 to 4 carbon atoms; and R2 is as defined above.
Aminoethylaminopropyltrimethoxysilane, aminoethylaminobutyltrimethoxysilane, aminoethylaminopropyltriethoxysilane, can be mentioned as representative of aminosilane compounds of formula (1-A).
While the polyaminopolyfunctional organosilanes are preferred, other polyfunctional organosilanes, such as vinylsilanes, acrylic silanes, methacrylic silanes, and the like, as described above, may be used in place of, or in addition to, the polyaminopolyfunctional organosilanes.
At least one other polyfunctional organosilane which is an epoxysilane, including any of the epoxysilanes as component (D) mentioned above, is also preferably included as one of the polyfunctional organosilanes of the primer coating composition. Especially, mention may be made of the glycidyloxy (C1-C6-alkyl)(tri-C1-C3 alkoxy) silanes, such as 3-glycidyloxypropyltrimethoxysilane, for inclusion in the primer coating composition.
Suitable amounts of the polyfunctional organosilanes in the primer coating composition, as solids (non-volatile silanol condensation products after addition of water) will generally range from about 1% to about 20%, by weight, preferably from about 2 to about 15%, more preferably from about 4 to 12%, by weight, of the composition. These amounts will typically, for a primer containing two of the polyfunctional silane compounds, correspond to from about 2 to about 40%, preferably from about 4 to about 30%, more preferably from about 8 to about 24%, by weight, of the total composition, in the as prepared composition, before water addition.
Thus, in a preferred composition containing a mixture of (a) polyaminoorganosilane and (b) glycidyloxyorganosilane, in appropriate volatile organic solvent, preferably isopropyl alcohol, the total amount of (a) plus (b) is preferably from about 5 to about 25 parts, more preferably, from about 10 to about 20 parts, per 100 parts of volatile organic solvent. Furthermore, weight ratios of (a):(b) in the range of from about 1:0.4 to 2, preferably 1:0.6 to 1.4, have been found to provide especially good results.
In use, the organic solvent, e.g., isopropyl alcohol, solution of the polyfunctional organosilanes, is thoroughly mixed with a small amount of water to catalyze the hydrolysis reaction. The resulting formulation is then generally ready to be applied to the substrate in from about 5 minutes to about 1 hour, typically, in about 10 to about 30 minutes, such as about 15 minutes.
Only a minor amount of water, such as from about 1 to 2 parts water per 100 parts of solution (e.g., from about 0.5 to 1.0 parts water per 10 parts polyfunctional silanes) will be sufficient to catalyze the hydrolysis reaction.
The primer composition may be applied to the substrate in any convenient manner, such as by wiping, brushing, dipping and spraying. Since the subject primer coating compositions do not form lumps, it is easy and convenient to apply by spraying, for example, using a number 4-6 nozzle with a pressure of about 20 psi. Preferably, the spray is in the form of a mist. It is not necessary to apply the composition uniformly since the coating will tend to flow together to provide a uniform continuous film.
Although the precise nature of the resulting primer coating is not known, it will be recognized by those skilled in the art that the polyfunctional silanes provide multiple reactive sites for adhering to the substrate, to itself and each other, as well as to the subsequently applied top coat.
Presumably, because of the strong adhesion to the substrate, resulting from the multiple reactive sites, the primer coating is extremely corrosion resistant, as will be shown from the examples provided hereinafter. Accordingly, the primer coating compositions of this invention can be used for many different applications where exposure to alkali and/or acid corrosive agents is anticipated, for example, in the automotive industry as a primer for resin paint finishes.
Generally speaking, the silane coating compositions according to the present invention have a broad scope of useful applications. The following are representative, but non-limiting, examples of applications in which one or more of the compositions, as described above, and in the following Examples, have been or may be used, with good results.
1. Protection of aluminum, steel, galvanized steel, stainless steel, brass, bronze, copper, silver, and other metals, from corrosive environments, including, as examples, salt water, hydrochloric acid, sulfuric acid, phosphoric acids, and the like.
2. Protection of interior and exterior building materials, such as, for example, ceramic roofing tiles, concrete, and galvanized steel, including interior surfaces of duct works, from deposition and growth of mildew and infectious organisms.
3. Overcoating and/or removal of graffiti from coated or uncoated concrete and metallic surfaces, without sacrificing the coating, when present.
4. Corrosion protection and maintenance of cooling and heating efficiencies of HVAC and other heat exchange equipment.
5. Corrosion resistant primer for various finishes, including, for example, urethane, epoxy, polyester, latex, and the like.
6. Overcoating for automotive and truck (e.g., cement truck), bus, and other vehicle, finishes.
7. Corrosion protection for food and beverage container surfaces in contact with foods, beverages, and the like, e.g., aluminum cans.
8. Overcoating and containing rust.
9. Coating fasteners, e.g., screws, bolts, rivets, and the like.
10. Barnacle release agent.
11. Protective, corrosion resistant and release surface, for manifolds, exhaust systems, cooking utensils, ovens, and other equipment exposed to temperature extremes.
12. Corrosion protection and/or deicing agent for aircraft wings and other surfaces.
13. Coating for glass surfaces in coastal environments to facilitate cleaning.
14. Wipe-on finish protector and refurbisher for automotive and other vehicle, equipment finishes.
15. Gel-coat maintenance finish.
16. Protective coating for maintaining asphalt tiles.
For any of the above applications, only thin coatings, on the order of about 2000 nm, or less, will provide good results. Generally, the coating compositions of the present invention are effective when applied to a coating (film) thickness (after cure) in the range of from about 5 to about 150 millionths of an inch, however, if desired to provide even superior corrosion protection, thicker films may be applied.